WR426 Help needed crankcase Airbox full of coolant?

Silverfox110

Hello all, My 2001 WR426 bargain bike, just rebuilt top end, and now I have coolant pouring out the flywheel plug and TDC inspection plug? Also airbox is full of coolant.

Decided to rebuild WR426 after recent bargain bike began using too much oil every ride, was "fill up the oil, and check the petrol"

Removed head as per Clymer manual and discovered so much carbon around valves and ex port, it would take me forever to clean.off everything, had a look on flebay for second hand head to use, only one I could find was YZ426 head and barrel from same year YZ , with owner stating low hours after rebuild. I bought them hoping they would fit Said head and barrel arrived, and head looked same as mine, but shiney, barrel looked ok too.

Had also recently purchased a Hot Cam exhaust cam and shim kit to replace the current exh with auto decomp, so seemed like the perfect time to do that as well.

Took both barrels (WR+YZ) to machine shop with new genuine std piston and ring set, shop measure both barrels and they are both unservicable? that was a surprise? Low hours from o/h? Left both cylinders at shop to re-sleeve the best one and I will pick up in week.

On the bench the YZ head with valves already installed, appears to be OK, recent carbon removal visible upon closer inspection, but all functions ok, The studs and dowells are fitted and cant remove them to check flatness, but steel ruler across all directions, doesn't reveal any problems, and the previous owner told me they were great condition! The YZ head came with cams and cam holders. The YZ inlet cam appeared to be in good condition, so went with that one, the WR cam covers were better that the YZ ones, so used them. The hotcams exhaust cam, brand new out of box. Test fitted valve caps, shimmed to correct clearance with cams installed.removed cams and holders and put them aside.

had left bottom end undisturbed, fitted piston rings, barrel, and YZ head as per manual used genuine WR426 head gaskets and seals. Only real issue in this process was getting the head onto cylinder whilst in bike frame with limited clearance, but all good at the end. Fitted cams, holders and torqued no surprise that clearance measured perfect as per bench setup. Installed external oil lines etc. Installed radiators and hoses, all simple and no surprises here. The front long water pipe from head fitted ok with new o ring, but very loose, continued the install.

Bike all back together with no plastics, new oil and filter, began to fill the coolant system, didn't check the fluid quantity in the book, but after a short time, leak began out the from long water tube in head, damn o ring leaking, drained system and replaced o ring with the one that was previously installed here, slightly thicker. refitted hoses etc. refilled system no leak from front o ring continued to pour more coolant into the filler waiting for to come to top, bottle empty 4 ltr still not at top, decided to have a look in side cover on flywheel (elec side) opened and out poured green liquid??? Spewed out all over my floor?? What the hell???? Looking into airbox, it is also half full with coolant???

Silverfox110

OK may have found something, was flushing engine oil system, had water pump impeller cover off, well what do you know, OIL pouring out everywhere??? Maybe water pump shaft and seal didnt like a short spell dry, while the engine being built, but I cant believe so much fluid can get past that little seal?

jojo1224

You shouldn't get coolant in the oil (or other way around) past the water pump seals because there is a weep hole on the bottom of the side cover. If the hole is plugged there is a chance but if it was going into the bottom end as fast as you can pour coolant into the rads I doubt it was the seals unless they are not even installed.

Silverfox110

Thanks, I have the same feeling, pulled the case cover removed impeller many marks all over shaft, and seals present, but dirty and worn. Have purchased new shaft and installed every seal in this area, put back together and almost to scared to fill the oil and see what happens. At least the water pump has been overhauled.

I doubt that that was the problem.

Could the oil have been coming from the water path in the case casting just above the impeller? therefore leak further up the line?

Still thinking about YZ head on WR gaskets?

Are there any markings on the head that would determine what year the YZ head could be from?

jojo1224

Thanks, I have the same feeling, pulled the case cover removed impeller many marks all over shaft, and seals present, but dirty and worn. Have purchased new shaft and installed every seal in this area, put back together and almost to scared to fill the oil and see what happens. At least the water pump has been overhauled.

I doubt that that was the problem.

Could the oil have been coming from the water path in the case casting just above the impeller? therefore leak further up the line?

Still thinking about YZ head on WR gaskets?

Are there any markings on the head that would determine what year the YZ head could be from?

Cheers
Foxxy

The YZ426 and WR426 heads are the same, just different cams. Don't fill it back up with oil and leave the drain plug out and fill the cooling system back up, you will know if the cooling system is leaking. The whole cooling system doesn't hold much, its a little over a liter if I remember correctly. Are the gaskets brand new? The head gasket is definitely non reusable.

Silverfox110

The YZ426 and WR426 heads are the same, just different cams. Don't fill it back up with oil and leave the drain plug out and fill the cooling system back up, you will know if the cooling system is leaking. The whole cooling system doesn't hold much, its a little over a liter if I remember correctly. Are the gaskets brand new? The head gasket is definitely non reusable.

OK just drained the oil, left the sump plug out, poured some coolant into the system 15 seconds or so, green coolant just poured out the oil drain? *(^*&^#%$! New head and cyl base gaskets, genuine yamaha ones. I still have the packets, I might just check the part numbers again